The present invention relates to powertrain mounts for motor vehicles, and more particularly to a powertrain mount having a controllable compliant member.
It is desirable to provide motor vehicles with improved operating smoothness by damping and/or isolating powertrain vibrations of the vehicle. A variety of mount assemblies are presently available to inhibit such engine and transmission vibrations. Hydraulic mount assemblies of this type typically include a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is separated into two chambers by a plate. A first or primary chamber is formed between the orifice plate and the body, and a secondary chamber is formed between the plate and the diaphragm.
The chambers may be in fluid communication through a relatively large central passage in the plate, and a decoupler may be positioned in the central passage of the plate disposed about the passage to reciprocate in response to the vibrations. The decoupler movement alone accommodates small volume changes in the two chambers. When, for example, the decoupler moves in a direction toward the diaphragm, the volume of the portion of the decoupler cavity in the primary chamber increases and the volume of the portion in the secondary chamber correspondingly decreases, and vice-versa. In this way, for certain small vibratory amplitudes and generally higher frequencies, fluid flow between the chambers is substantially avoided and undesirable hydraulic damping is eliminated. In effect, the decoupler is a passive tuning device.
As an alternative or in addition to the relatively large central passage, an orifice track is normally provided. The orifice track has a relatively small, restricted flow passage extending around the perimeter of the orifice plate. Each end of the track has an opening, with one opening communicating with the primary chamber and the other with the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the decoupler, provides at least three distinct dynamic operating modes. The particular operating mode is primarily determined by the flow of fluid between the two chambers.
More specifically, small amplitude vibrating input, such as from relatively smooth engine idling or the like, produces no damping due to the action of the decoupler, as explained above. In contrast, large amplitude vibrating inputs, such as large suspension inputs, produce high velocity fluid flow through the orifice track, and an accordingly high level of damping force and desirable control and smoothing action. A third or intermediate operational mode of the mount occurs during medium amplitude inputs experienced in normal driving and resulting in lower velocity fluid flow through the orifice track. In response to the decoupler switching from movement in one direction to another in each of the modes, a limited amount of fluid can bypass the orifice track by moving around the edges of the decoupler, smoothing the transition.
Prior decoupled powertrain mount designs therefore employ a decoupler that is dependent of vibration amplitudes/frequencies during compressions of the mount during fluid flow through the orifice plate. In some vehicle states, such as high-speed shake, it is advantageous to provide damping for small amplitude vibrations. During high-speed shake conditions, small imbalances in the vehicle""s wheels excite the powertrain, which result in vibrations inside the cabin of the vehicle. By controlling the powertrain, providing damping, the vibrations inside the cabin of the vehicle are reduced.
For small mount displacements the dynamic stiffness of the mount is approximately the same as the static stiffness of the mount. Ideally, for isolation functions of a powertrain mount, the dynamic rate at the disturbance frequency should be as low as possible. Therefore, it is also desirable to lower the dynamic rate of the mount below a static rate of the mount at engine disturbance frequencies.
Prior powertrain designs also incorporate the use of a single orifice track to control both isolation and damping functions. Such designs require the powertrain mount to change between functions when some engine and environment conditions require both functions simultaneously. For example, a single-track orifice plate must change from bounce control (at around 10 Hz) to isolation (which starts at approximately 20 Hz).
It is desirable, therefore, to provide a powertrain mount that overcomes these and other disadvantages.
The present invention is a powertrain mount comprising an orifice plate including two tracks, a control track and an isolation track. The control track includes a fixed spirally formed track within the orifice plate, which has an exit and entrance on either side of the plate. The isolation track is formed between an alignment plate and rotatable track member, each having an exit and entrance respectively. The rotatable member and the alignment plate are sealingly engaged and affixed to a decoupler and an annular area disposed about the orifice plate of the powertrain mount. The exit of the alignment plate is adjacent the decoupler. The rotatable member with the orifice plate forms a cavity with a molded body of the powertrain mount, with the entrance of the rotatable member exposed to fluid within the cavity for controlling and minimizing vibrations within the powertrain. The isolation track has a track length that may be varied by rotation of the track member and its entrance. Various magnitudes of disturbance frequencies may be managed and controlled by either the fixed control track and/or the variable isolation track within the powertrain mount.
Accordingly one aspect of the invention includes rotation of the rotatable member and its entrance changes the length of the variable track. A motor operably connected and adapted to the rotatable member to rotate the rotatable member based on vibration frequencies. Rotation of the rotatable member changes the length of the variable track and allows fluid flow through the entrance of the rotatable member, along the isolation track, and to the decoupler via the exit of the alignment plate.
Another aspect of the present invention is to provide a powertrain mount of the type described above that improves isolation and damping of the mount at particular vibration disturbance frequencies. Still another aspect of the present invention is to provide a powertrain mount of the type described above in which specific ranges of amplitude frequencies of the powertrain are isolated or damped by selectively rotating the rotatable member to engage the decoupler member within the isolation track, while the control track passively controls other discreet vibrations.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.